The invention relates to a device for dispensing of a powdered drug preparation by inhalation. The device is in particular a multiple-dose device without propellant gas, equipped with a metering means which dispenses doses from a powder container. A device such as this is usable, for example, in the treatment of asthma.
The administering of a powdered drug preparation by inhalation from an inhaler is commonly known. Multiple-dose type powder inhalers comprising a flow container which holds the drug and a metering member which measures and dispenses a unit dose are also known, for example from patent publications GB 2165159, EP 79478, and EP 166294. In these devices, a series of dosing recesses are notched into the surface of a cylindrical metering member, and the said member is disposed in a chamber of precisely the same shape. When the metering member is rotated, the dosing recesses in turn will move first to a position in alignment with the powder container for being filled and thereafter to a position in alignment with the inhalation channel, whereupon a unit dose will fall by gravity from the dosing recess into the inhalation channel. Thereafter the dose of medicament is inhaled from the inhalation channel. These devices have the drawback that they make overdosing of the medicament possible by allowing the dispensing of a plurality of doses in succession into the inhalation channel, whereby a multiple dose may be drawn by one inhalation.
Attempts have been made to solve the above-mentioned problem by using dispensing systems in which the dosing recess will not be emptied into the inhalation channel by gravity but, instead, the dose of medicament is inhaled directly from the dosing recess, such recesses having been notched into the surface of a metering member having the shape of a cylinder, a cone or a truncated cone, as disclosed in patent publications WO 92/00771 and WO 92/09322. Also in these devices, a metering member having the shape of a cylinder, a cone or a truncated cone is disposed in a chamber having precisely the same shape. When the metering member is rotated, the dosing recesses will move first to a position in alignment with the flow container for filling, and then to the inhalation channel, which is shaped so that the dosing recess will be emptied under the effect of the air flow being inhaled, and thereafter, having rotated through a full 360.degree., back to a position in alignment with the flow container. Since the metering member is, for purposes of metering precision, disposed within a chamber of the same shape, and since it has to be rotated through 360.degree., most of which is futile for the actual function of the inhaler, in such devices the metering member may be prone to jamming as powder falls onto the surfaces of the device.
In patent publications WO 92/00771 and WO 92/09322 referred to above there is additionally disclosed a counter system the purpose of which is to indicate the quantity of unit doses which remain in the inhaler or which have already been used. The operating mechanism of these counters is linked to the rotary movement of the metering member, which movement is transmitted to a geared counting disk or coiled strip. The disc or strip is equipped with markings which can be seen on the outside of the inhaler. The said counters thus in fact indicate how many times the metering member has been moved to the inhalation channel or how many times the inhaler has been activated for inhalation. However, the patient may for various reasons activate such an inhaler also without the purpose of inhaling, in which case the unit dose is ultimately returned to the powder container. Thus the said counters do not always indicate the real number of remaining unit doses.